1. Field of the Invention
The present invention relates to an image forming apparatus that controls a driving unit configured to drive a conveyance unit, which is configured to convey a recording material.
2. Description of the Related Art
A conventional image forming apparatus has the capability of increasing or decreasing the conveyance speed of each recording material to convey recording materials at optimum intervals in image forming processing. To convey a recording material to a transfer position at ideal timing, the acceleration/deceleration control includes detecting the recording material with a sensor disposed on a conveyance path. The acceleration/deceleration control further includes obtaining a difference between the detected arrival timing of the recording material and ideal arrival timing. The acceleration/deceleration control further includes increasing or decreasing the conveyance speed in such a way as to reduce unevenness, such as advanced/delayed pickup or slippage occurring during a conveyance operation, to convey the recording material to the transfer position at ideal timing.
In general, a driving source of a recording material conveyance unit is a stepping motor or a direct current (DC) motor. The stepping motor is desirably used in feed-forward control because the stepping motor can cause an angular movement in proportion to the number of pulses of an input signal. In other words, the stepping motor is excellent in speed and position controllability compared to a DC motor used in feedback control. From the reason described above, the stepping motor is desirably employable as the driving source of the conveyance unit. On the other hand, the DC motor is a recently employed driving source for a recording material conveyance unit because the conveyance speed tends to increase and the required torque of the driving source tends to increase. For example, a conventional method discussed in Japanese Patent Application Laid-Open No. 2004-88926 includes generating an ideal profile for a driving operation, when the driving operation is performed, based on a target position and predetermined parameters, in the control of a DC motor employed as a power source for a device driving a mechanism, and controlling the driving of the DC motor according to the generated profile.
As conventionally known, when a DC motor is employed as a driving source, it is feasible to obtain a large torque. However, in an image forming apparatus, an optimum control method for controlling the conveyance speed of a recording material is variable depending on each control period in the process of conveying the recording material. Therefore, if a DC motor or a comparable driving source requiring feedback control is employed to perform conveyance control with fixed control constants in any control period, it is unfeasible to perform optimum control according to a conveyance state of the recording material. It is difficult to accurately control the conveyance speed of the recording material.